Traditionally, containers for chemically sensitive materials have been made from inorganic materials such as glass. Glass containers offer the advantage that they are substantially impenetrable by atmospheric gases and thus provide a product with a long shelf life. Glass containers are also readily recyclable. However, glass containers are heavy and expensive to manufacture.
More recently, lighter and less expensive containers made of polymeric materials are being used in applications where traditionally glass containers were used. These polymeric containers are less suspectable to breakage, are less expensive to manufacture, are lighter and less expensive to ship than glass containers. Further, polymeric containers can be made transparent thus allowing the contents of the container to be readily viewed by a consumer before the product is purchased.
However, polymeric containers are not without disadvantages. One significant disadvantage is that polymeric containers are ordinarily highly permeable to gases. This high permeability to gases allows atmospheric gases to pass through the polymeric container to the packaged product and also allows gases in the packaged product to escape through the polymeric container, both of which undesirably degrade the quality and shelf life of the packaged product.
One approach to decrease the gas permeability of polymeric containers is to form a multilayered polymeric container which includes at least one low gas permeable polymeric layer along with at least one other polymeric layer. However, such an approach is relatively complicated, costly and often produces a container which is difficult to recycle.
Another approach to decrease the gas permeability of polymeric containers is to deposit a barrier coating, i.e. a coating having a substantial resistance to the permeation of gaseous or volatile material, on the polymeric container. To date however, there are several obstacles which have prevented barrier coated polymeric containers from gaining wide acceptance.
One obstacle which has inhibited the use of barrier coated polymeric containers is that conventional barrier coating deposition techniques are not well suited for mass production. To illustrate, in Thomas et al., U.S. Pat. No. 5,378,510 a method and apparatus for depositing barrier coatings on the interior surface of a polymeric container is presented. However, in Thomas et al., a tubular plasma chamber 46 with downstream extension 52, adaptor 50, tube 54 and coaxial conduit are employed to convert an oxidizing gas into a plasma and to deliver the activated oxidizing gas species separately from organosilicon vapor to the vicinity of the article to be coated (see col. 6, lines 46-67 and FIG. 1). Thus, although Thomas et al. demonstrates the feasibility of depositing a barrier coating on an article, the tubular plasma chamber and associated equipment are relatively expensive and complex and thus are not well suited to the production environment.
Another obstacle which has inhibited the use of barrier coated polymeric containers is the difficulty associated with depositing a uniform barrier coating. Generally, it is preferable to deposit a uniform barrier coating on the polymeric container to ensure that the entire polymeric container provides an effective gas permeation barrier.
One conventional technique to improve the uniformity of the deposited barrier coating is to rotate the container during processing. To illustrate, in Thomas et al. at col. 9, lines 14-20 the polymeric container is rotated during the deposition of the barrier coating to promote the even distribution of the barrier coating on the interior surface of the polymeric container. However, as rotation of the polymeric container is accomplished using an additional motor which rotates a shaft extending into the chamber through an air to vacuum feedthrough, rotation of the polymeric container further increases the cost and decreases the reliability of the barrier coating deposition process.
Accordingly, the art needs a simple, inexpensive and reliable process for depositing a barrier coating on a polymeric container. The process should have a fast cycle time to accommodate production demands. Further, the barrier coating deposited should have good uniformity without the necessity of rotating the polymeric container and the barrier coated polymeric container should be readily recyclable.